Study On Control Technology Of Dynamic Voltage Restorer

With the increasingly rise of industrialisation,electric power load increases sharply,which makes the network appeared a wide range of power quality problems.According to statistics and analysis of the national scholars and the power department,voltage sag is one of the highest probability power quality problems in power system.DVR is a power electronic device to compensate the voltage,emerging in recent years,concatenating between power and sensitive loads,has a good dynamic characteristics.When the voltage sag occurs,it can compensate voltage sag effectively in millisecond.It is an effective device which can inhibit the dynamic voltage disturbances and can inhibit the harmonic interference and voltage flicker in power supply voltage.The analysis and research based on the basic structure and working principle of DVR based on voltage detection method,compensation control strategy and control method is studied.In the detection aspect,this paper first gives a brief introduction to the traditional detection methods,and on this basis,this paper carried out the theoretical derivation of method for detecting voltage phase zeroing,finally,the simulation analysis is carried out,the simulation results show that the phase zero method is feasible.In compensation aspect,firstly,this paper introduces the traditional compensation strategy,then the basic principle of minimum energy compensation strategy is introduced in detail,and the concept of compensating power circle is also introduced to illustrate the relationship between the compensation level and the voltage sag,finally,this paper uses the power system simulation software PSCAD to build model.It successfully establishes a model for each component of the DVR.Then proceed to the simulation of single phase voltage sag.Finally,simulation results to achieve the desired compensation effect.In the control aspect,firstly,the traditional control methods are summarized and classified,and on this basis,this paper chooses the improved feedforward control method,which is in the closed loop control method based on coupled with feedforward correction,and also added to the forward channel integral control link.Then the transfer function of the improved feedforward control method and the transfer function of open-loop control are studied and compared,and the Bode diagram and the unit step response diagram are obtained respectively.Finally,the improved feedforward control method is simulated,and the simulation results verify the feasibility of the improved feedforward control method.